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Purpose: The brachialis (BM) is a complex muscle with a long-running controversy regarding its morphology and innervation. The primary objective of this study was to elucidate the detailed gross morphology of BM in an adult Sri Lankan population., Method: Cadaveric upper limbs (n = 240) were examined for the proximal and distal attachments, length, width, thickness of BM, and innervations by the musculocutaneous (MCN) and radial nerve (RN)., Results: In all cases, the BM consisted of two heads: superficial head (SHB) and deep head (DHB). Proximally SHB and DHB originated from the lateral, anterior, and medial aspects of the middle and distal thirds of the shaft of the humerus and inserted onto the coronoid process and the tuberosity of ulna, respectively, as two separate entities. Statistically significant (P < 0.05) gender differences were observed between the mean values (mm) of muscle length (male: 188.03 ± 10.54; female: 166.14 ± 7.97), width (male: 26.57 ± 4.80; female: 25.28 ± 4.67), thickness (male: 10.73 ± 1.74; female: 9.74 ± 1.28), and tendon length (male: 44.44 ± 7.73; female: 33.40 ± 5.09). In all cases, MCN innervated the BM, while the model site of piercing was in the middle third of the muscle. The incidence of RN contribution to BM was 83.33% and in the vast majority it pierced the inferior third of the BM., Conclusion: Present study provides a comprehensive anatomical overview of the BM. An in-depth knowledge of the anatomy of BM may aid in comprehending functional characteristics, enhance the accuracy of imaging modalities, and provide new insight to the current surgical approaches around the elbow joint which in turn will invariably minimize the potential complications encountered during clinical procedures.

Purpose: Coracobrachialis (CBM) is a complex muscle with a wide range of variations in its morphology and innervation. The goal of this study was to elucidate the morphology, morphometry, gender differences of CBM and precise anatomical position of the musculocutaneous nerve (MCN) with reference to surrounding anatomical landmarks in an adult Sri Lankan population., Method: Cadaveric upper limbs (n = 312) were examined for the proximal and distal attachments, length, width, thickness of CBM and its relationship with the MCN., Results: The CBM originated from the tip of the coracoid process of the scapula and lateral, posterior and medial aspects of the tendon of short head of biceps brachii. Gender differences were observed in all morphometrical parameters of CBM. In 83.33 %, MCN perforated the CBM. In 50 % the MCN pierced the middle one-third of CBM while none pierced the lower one-third. The distance from the coracoid process to the point of entry of MCN into CBM (distance P) was 50.62 mm. A positive correlation was observed between the arm length and distance P indicating that arm length provides an accurate and reliable means of gauging the distance P of an individual., Conclusion: The present study provides new evidence pertaining to the origin of CBM. Further, it was revealed that the predicted distance P of any upper extremity can be calculated by dividing the arm length by 5. Precise anatomical location of MCN in relation to CBM using unequivocal and well-defined anatomical landmarks will be imperative in modern surgical procedures.